Technical Field
The instant disclosure relates to a capacitive sensing technology, and more particularly, to a method for detecting background signals of a capacitive sensing device.
Related Art
For the sake of improving convenience of usage, more and more electronic devices adopt touch screens as operating interfaces. A user can touch graphics displayed on a touch screen of an electronic device for manipulating the electronic device. Comparing to button-based manipulations or other manipulation methods, touch-based manipulations are quicker, more convenient, and more ergonomic. The touch screen mainly includes a display device providing a displaying function and a sensing device providing a touching function.
These sensing devices can be classified, according to the structures and the principles applied, into several sensing types such as resistive sensing, capacitive sensing, acoustic sensing, optic sensing (e.g., infrared ray sensing), and electromagnetic sensing. Specifically, the capacitive sensing devices (i.e., sensing devices belonging to capacitive sensing type) do not require materials having good properties in terms of stress and strain, and are not easily affected by environment light. Furthermore, the manufacturing process of the capacitive sensing devices is simpler than other types of sensing devices. Therefore, most of touch screens which are recently manufactured intend to adopt the capacitive sensing device for the touch-based manipulation.
The capacitive sensing device includes sensing points which are defined by X electrodes and Y electrodes and are configured in an array form. When the user touches the capacitive sensing device, a capacitance value of at least a corresponding sensing point on which the user touches changes, and then the capacitive sensing device identifies that a touch manipulation occurs by detecting changes of the capacitance value of the sensing point. During operation, the capacitive sensing device stores background signals (i.e., capacitance values of untouched sensing points) of each sensing point as a reference value, and compares capacitance value sensed by every sensing point with the reference value so as to identify whether a certain position is touched.
Each capacitance value corresponds to each sensing point in the array. When the resolution of the display device raises (i.e., the number of the sensing points raises), the capacity of the memory utilized for storing the capacitance values accordingly requires to be enlarged, and the time consumed by updating the reference value also accordingly becomes longer. Consequently, the reference value cannot be updated frequently in a proper way and the promptness of a signal-reading process is reduced. If the reference value needs to be updated more frequently by lowering the reading frequency regarding the signal-reading process, it brings a negative effect on the sensitivity and the accuracy regarding the detection of the touch manipulation and the efficiency of the entire system declines.